This invention relates to a knife holder for a knife tool head that can be assembled with chipping knives on the periphery and slabbing knives on the ends, where the knife holder has a mounting face for a chipping knife and an adjacent mounting face inclined to the former for a slabbing knife and knife mounting means for detachable mounting of the chipping knife and the slabbing knife on the respective mounting face; this invention also relates to a respective knife and a knife tool head having a base body in the form of a truncated cone or a cylinder and multiple knife holders attached thereto with one or more knives mounted on each.
Such knife tool heads are used, for example, for chipping wood, in particular for chipping the lateral segments of logs in profile chippers and choppers in the production of wood chips for papermaking. Chipping knives are used primarily to produce the useful chips, while the slabbing knives, also known as planing knives, serve primarily to produce a flat smooth surface on the remaining wood material.
U.S. Pat. Nos. 5,271,442 and 5,709,255 disclose generic knife holders designed in a U shape with a base plate that is provided with boreholes for screwable attachment to the lateral surface of an essentially cylindrical base body of the tool head. A buckling U-shaped section that is elevated from the base plate supplies the two mounting faces for the chipping knife and the slabbing knife, namely as planar surfaces provided with boreholes. Turning knives are used as the chipping knives and slabbing knives; each knife is secured between a respective carrier, which is in contact with the respective mounting face of the holder, and an outer clamping piece. For assembly, the carrier is first screwed to the mounting face of the holder, and then the chipping knife or slabbing knife is placed on top of that and next the clamping piece is applied and attached to the holder with screws at fastening points at the side next to the knife, with the screws passing through through-bores in the carrier.
Another generic knife holder is disclosed in Unexamined German Patent DE 198 16 164 A1, wherein chipping knives and slabbing knives are secured on the holder and clamped in the same way using a clamping piece and a carrier. The knife holder there has a flange with a dovetailed cross section with which it can be secured on a hub element that functions as the base body of the tool head. The hub element in the form of a cylindrical ring therefore has flattened areas on the outer lateral surface with longitudinal grooves introduced into them, so that a knife holder with its flange can be inserted axially into each longitudinal groove and secured there.
The chipping knives and slabbing knives of the turning knife type used with the generic knife holders mentioned above have a rectangular basic shape, i.e., their transverse and/or narrow sides run in planes perpendicular to the longitudinal edge knife cutting edges. In application cases in which the longitudinal axes of the chipping knife and slabbing knife are in different planes, i.e., in which the chipping knife leads or trails behind the slabbing knife in the direction of rotation of the tool head, the chipping knife and the slabbing knife are in mutual contact on their facing ends of the free active knives only at some points when in the new state. Due to wear and in particular due to regrinding of the knife cutting edges, the case may therefore occur when the point contact of the active knife cutting edges of the chipping knife and the slabbing knife are lost, the result being a continuous gap between the chipping knife and the slabbing knife, which can become clogged with wood fibers or chips in an undesirable manner during operation.
German Patent DE 198 58 740 C1 describes mounting a knife on a knife holder which has a mounting face with holder contact faces that are inclined in a V-shaped cross section, where the knife is in contact with corresponding inclined knife contact faces in a V-shaped cross section. The knife is held directly on the knife holder and thus without the use of clamping pieces due to the respective knife mounting means with a holding force that acts in the area between the contact faces, which are inclined in a V shape.
This invention is based on the technical problem of providing a knife holder which can be assembled with chipping knives on the periphery and slabbing knives on the end face, a knife for this holder and a respective knife tool head which will jointly permit secure, self-centering holding of one chipping knife and one slabbing knife jointly on a holder without any play. This holder can in turn be secured on the tool head and allows relatively simple replacement of the knives without any complex adjustment work, whereby the chipping knife and the slabbing knife can also be mounted on the holder with the knives in close proximity even in the reground state if necessary.
With the inventive knife holder, the two mounting faces for the chipping knife and the slabbing knife each have holder contact faces that are inclined to form a V-shaped cross section, and direct fastening means are provided as the knife mounting means, securing the chipping knife and the slabbing knife, each having knife contact faces forming a corresponding V shape, directly on the respective holder contact face with a holding force acting between the contact faces that are inclined in a V shape.
The line of action of the holding force for the chopping knife as well as that of the slabbing knife are each in the angle range spanned by the contact faces inclined in a V shape, so that a self-centering effect of the two knives when secured on the knife holder is obtained due to the effect of the holding force. The centered position is unambiguously defined for each of the two knives by the pairs of cooperating contact faces inclined in a V shape and opposing one another with respect to the line of action of the holding force. The holding force which acts in this way also results in a uniform force distribution on these contact faces and thus on the whole in a favorable uniform fastening force acting on the respective knife and the knife holder. These characteristic properties of direct holding of the chipping knife and the slabbing knife on a common holder consequently ensure a secure mounting of the chipping knives and the slabbing knives on the tool head without any play even under load during chipping operation and thus permit a rapid and easy mounting of the knives with a high repeating accuracy of the knife position on insertion of a new knife without requiring complex adjustment work.
With the inventive knife holder, the chopping knife and the slabbing knife are attached directly to the respective mounting face and the holding body is designed as a one-piece part and can in turn be attached directly to the knife tool head. Consequently, this permits very simple mounting of the chopping knife and the slabbing knife onto a joint one-piece holder body and dismantling it therefrom as well as mounting the holder body on and/or dismantling it from the knife tool head with direct fastening means without additional parts.
In an advantageous embodiment of this invention, the direct fastening means consist of a single screw connection for the slabbing knife and one or two screw connections for the chipping knife. Beyond this, no additional fastening parts such as clamping pieces or the like are necessary.
Advantageous positioning of chipping knife and slabbing knife in relation to one another is provided by an embodiment in which there are corresponding angle ranges which describe the relative position of the cutting edges of the chipping knife and slabbing knife.
In a further refinement of this invention, holder fastening means for the knife holders are provided laterally next to the mounting faces for the knives. In this way the holders can be mounted on the tool head without being hindered by the knives and dismantled from it again without having to remove the knives from the holder.
Another embodiment of the inventive knife is designed so that it has one or two inclined contact areas on at least one transverse side, these contact areas extending from one end of the knife cutting edge with a slope that corresponds to a corresponding inclined angle of the relative position of the peripheral knives and the slabbing knives on the holder, so that when the knife is mounted on the holder as a chipping knife or as a slabbing knife, it is in contact with the other knife not only with spot contact but instead with linear or area contact with this area. The chipping knife and slabbing knife may be provided with the corresponding slopes or the slope may be provided completely on one knife, in which case the other knife then has a transverse edge perpendicular to the knife cutting edge. The linear or surface abutment of the two knives in an area in contact with the active cutting edges yields the advantageous effect that the two knives are always in mutual contact without any essential gap on their active knife cutting edges even in a used, reground state, so that there is no unwanted clogging or jamming of chipped material between the two knives in the meantime.
With another embodiment of the inventive knife tool head, multiple inventive knife holders are distributed on the circumference of a base body in the form of a truncated cone. They are inserted here in the respective holder receptacles, where the chipping knives point toward the lateral surface of the truncated cone of the base body and the slabbing knives point toward the end face of the base body.
In a further refinement of this invention, multiple second knife holders are provided on the lateral surface of the base body of the tool head in the form of a truncated cone behind said inventive knife holders, each being assembled with a chipping knife and a slabbing knife, and are offset with respect to these in the circumferential direction, whereby the second knife holder is assembled with only one chipping knife. It is found that the knife tool head designed in this way fulfills very well the cutting function as well as the smoothing function.
In another embodiment of this invention, the knife tool head is assembled with two different types of inventive knife holders which differ in chipping knives of different lengths. The two different types of knife holders are arranged in a preselectable regular sequence in the circumferential direction of the tool head base body. Here again, it is found that such a knife tool head fulfills very well the functions of chipping and smoothing at the same time, as expected of it.
In a further embodiment, the slabbing knives of two or more knife holders mounted on the tool head sequentially in the direction of rotation are arranged with slabbing knives and chipping knives in planes that are offset axially in relation to one another. This yields a certain desired chip thickness according to the axial spacing between such successive slabbing knives.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.